The present invention relates to a device for exposing a thermal stencil sheet to a source of infrared rays and, more particularly, to an exposure device for a thermal stencil sheet which has an infrared ray absorbent image directly provided thereon.
As a method of perforating a thermal stencil sheet, it is known to provide an infrared ray absorbent image directly on a thermal stencil sheet by handwriting or by employing suitable duplicating means and to expose this thermal stencil sheet having the infrared ray absorbent image to a source of infrared rays so that the thermal stencil sheet is perforated in accordance with the image by the heat generated in the image due to absorption of infrared rays. Therefore, in contradistinction to an orthodox method of perforation for a thermal stencil sheet in which the thermal stencil sheet is pressed onto an image surface of an original while infrared rays are projected onto the image surface through the thermal stencil sheet so that the heat generated in the image portions of the original due to absorption of infrared rays is effectively transmitted to the thermal stencil sheet for effecting its perforation, it is not required to apply any pressing force to the aforementioned thermal stencil sheet having an infrared ray absorbent image directly provided thereon while it is exposed to a source of infrared rays for thermal perforation.
Thermal stencil sheets which are suitable for use with the aforementioned method of providing an infrared ray absorbent image directly thereon are disclosed in the co-pending patent applications Ser. Nos. 854,676 and 854,677 filed by applicant on Nov. 25, 1977 for/by the same assignee/applicant as the present application.
In order to effect uniform and proper perforation in a thermal stencil sheet directly provided with an infrared ray absorbent image, the thermal stencil sheet must be exposed to uniform radiation of infrared rays over the entire region thereof. Such an exposure can of course be performed by employing a conventional thermal stencil sheet duplicating device of the type having a transparent rotary cylinder made of glass which cooperates with an endless belt for transferring a sheet around the rotary drum so as to expose the sheet to infrared rays irradiated from a linear tungsten lamp provided along the axis of the rotary cylinder, or of the type having a flat exposure window defined by a flat glass panel to which infrared rays are radiated from an electronic flash discharge tube or tubes with the help of a reflector. However, these conventional duplicating devices are intended to be used for a duplicating process such as irradiating infrared rays onto a lamination of a thermal stencil sheet and an original while pressing the thermal stencil sheet onto the original by the provision of the transparent glass rotary drum or panel, and as a consequence, in these devices the infrared rays are radiated onto the thermal stencil sheet through a layer of glass, thereby inevitably causing a loss of energy of infrared rays. Furthermore, unless such a conventional device is already available for the purpose of performing the conventional thermal stencil sheet duplicating process, a relatively high cost is incurred in obtaining such a conventional device in order to perform a simple exposure of a thermal stencil sheet directly provided with an infrared ray absorbent image to radiation of infrared rays without requiring any application of pressing force thereto.